Thermal Compensation in an Integrated Image Sensor and Lens Assembly

ABSTRACT

An integrated image sensor and lens assembly comprises a lens barrel holding camera lenses coupled to a lens mount. The lens mount is further coupled to an image sensor substrate that has an image sensor lying on an image plane. The optical distance between lenses and the image sensor is tuned such that the focal plane of the lenses coincides with the image plane. Due to thermal expansion, this optical distance may vary thereby to cause the focal plane of the lenses to shift away from the image plane. The integrated image sensor and lens assembly further comprises spacers that couple one or more lens elements to the lens barrel. The spacers and the lens elements are configured such that the optical distance is maintained to be constant or substantially constant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/141,673 filed Apr. 1, 2015 and of U.S. Provisional Application No.62/160,473 filed May 12, 2015, both of which are hereby incorporatedherein by reference in their entirety.

BACKGROUND

1. Technical Field

This disclosure relates to a camera, and more specifically, to thermalcompensation in integrated image sensor and lens assemblies.

2. Description of the Related Art

Manufacturing of lens assemblies for high-resolution cameras typicallyrequire a high degree of precision in positioning components of the lensassembly to ensure that the lens will achieve proper focus. As a result,a challenge exists in achieving a fast, automated, and high-yieldingassembly process for high-resolution cameras.

In an integrated image sensor and camera lens system, a lens is coupledto an image sensor. A camera lens includes one or more lens elements. Acamera lens can be coupled to the image sensor with a single-pieceintegrated mount or an assembly of at least a barrel holding the lenselements and a mount positioning the barrel with respect to the imagesensor such that the image sensor is properly aligned with the lens tomaintain image quality. For example, in a “permafocus” design, thecamera lens is rigidly coupled to the image sensor after some alignmentprocedure.

The integrated system is susceptible to changes induced by environment.For example, camera lenses tend to defocus due to a temperature change.The defocus is a result of several factors, including thermal expansionof the lens elements, change in index of refraction of the lenselements, and thermal expansion of the barrel/mount and other componentsof the assembly. Thermal expansion is a function of the temperaturechange and the coefficient of thermal expansion (CTE) of the material.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed embodiments have other advantages and features which willbe more readily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an exploded view of an integrated image sensorsubstrate and camera lens system configuration, according to oneembodiment.

FIG. 2 illustrate an example spacer coupling (e.g., mounting) a lenselement to a lens barrel, according to one embodiment.

FIG. 3 illustrate an example spacer coupling (e.g., mounting) a lenselement to a lens barrel, according to one embodiment.

FIG. 4 illustrate an example spacer coupling (e.g., mounting) a lenselement to a lens barrel, according to one embodiment.

FIG. 5 illustrates an example camera that includes the integrated imagesensor and lens assembly, according to one embodiment.

DETAILED DESCRIPTION

The figures and the following description relate to preferredembodiments by way of illustration only. It should be noted that fromthe following discussion, alternative embodiments of the structures andmethods disclosed herein will be readily recognized as viablealternatives that may be employed without departing from the principlesof what is claimed.

Reference will now be made in detail to several embodiments, examples ofwhich are illustrated in the accompanying figures. It is noted thatwherever practicable similar or like reference numbers may be used inthe figures and may indicate similar or like functionality. The figuresdepict embodiments of the disclosed system (or method) for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles described herein. Those skilled in the art willappreciate that structures and methods described herein may beimplemented in devices such as cameras and projectors.

In the assembly process, the focal plane of the lens is aligned with theimage plane of the sensor. Lenses can be designed, to some extent,including materials that have favorable thermo-optic coefficients. Thebarrels, mounts, and other mechanical parts can be made of materialswith the required coefficients of thermal expansion (CTEs) to keepthermal performance changes within some pre-defined tolerance. However,manufacturing and cost limitations sometimes necessitate a less thanoptimal material selection, and this results in a movement of the focalplane relative to the image plane as a function of temperature. In acamera lens including multiple lens elements, the position of the focalplane is more sensitive to some elements than others. Thus, it ispossible to manipulate the position of the focal plane by moving certainlens elements relative to the others. When the defocus problem is due totemperature, this can be achieved passively by prescribing a particularthermal expansion between two or more lens elements which is differentthan the thermal expansion of the barrel holding the lens elements inplace, effectively moving one or more lens elements in a differentdirection and/or magnitude with respect to the others. This manipulationcan result in a net movement of the focal plane relative to the imageplane which is within some pre-defined tolerance without otherwisecausing detriment to the image quality. The pre-defined tolerance canbe, for example, a percentage tolerance in the modulation transferfunction (MTF), physical size of the circle of least confusion, aparticular fraction of the Rayleigh range at the primary wavelength,etc.

Often times, lens assemblies include spacers to mechanically locate lenselements in the barrel. In such designs, the spacer CTE and dimensioncan be chosen so as to favorably manipulate the focal plane position asa function of temperature. However, this change can also be achieved bylocal changes in temperature, for example, by routing system heat to aparticular location in the lens assembly, or by actively heating andcooling different sections of the assembly.

An integrated image sensor and lens assembly comprises a lens barrelholding a set of camera lens elements coupled to a lens mount. The lensmount is further coupled to an image sensor substrate that has an imagesensor lying on an image plane. The optical distance between the set oflenses and the image sensor is tuned such that the focal plane of thelenses coincides with the image plane. Due to thermal expansion of thelens barrel and the lens mount, the optical distance between the lenselements and the image sensor may vary thereby to cause the focal planeof the set of lenses to shift away from the image plane. The integratedimage sensor and lens assembly further comprises one or more spacersthat couple a subset of the set of lens elements to the lens barrel. Thespacers and the subset of the set of lens elements are configured suchthat the optical distance between the set of lens elements and the imagesensor is maintained to be constant or substantially constant. Asdescribed herein, substantially constant refers to the optical distanceis within a predefined tolerance that would be acceptable to thoseskilled in art. In various embodiments, the predefined tolerance can be,for example, a 1% tolerance, a 2% tolerance, a 5% tolerance, etc. Thespacers may move the subset of lens elements in such a way that theoptical distance of the set of lens elements and the image sensor ismaintained to be constant or substantially constant. In response to atemperature change, the motion of the subset of lens elements may be ata different magnitude and direction with respect to the rest of the lenselements.

FIG. 1 illustrates an exploded view of an embodiment of an integratedimage sensor substrate and camera lens system configuration 100 thatincludes a camera lens barrel 110, a camera lens mount 120, one or morespacers 150-151, and an image sensor substrate140. The image sensorsubstrate140 has an image sensor assembly 130 (e.g., a high-definitionimage sensor) for capturing images and/or video. The camera lens mount120 is physically affixed to the image sensor substrate 140 and alsoaffixed to the camera lens barrel 110.

The lens barrel 110 comprises one or more lens elements or other opticalcomponents 112 to direct light to the image sensor assembly. The lensbarrel 110 is affixed to the lens mount 120 with a threaded joint 114positioned to minimize the thermal shift of the focal plane relative tothe image plane 171. The lens barrel 110 comprises a lower portion 116,one or more barrel arms 114, and a lens window (which may be one of thelens elements 112). The lower portion 116 of the lens barrel 110 issubstantially cylindrical and structured to at least partially extendinto the channel of the tube portion 128 of the camera lens mount 120.The barrel arms 114 extend radially from the body of the lens barrel 110and are outside the channel of the lens mount 120 when assembled. Thelens arms 114 may be used to physically couple the lens barrel 110 tothe camera body (not shown). The lens window includes optical componentsto enable external light to enter the lens barrel 110 and be directed tothe image sensor assembly 130. The camera lens mount 120 includes a tubeportion 128 that extends away from the image sensor assembly along theoptical axis 170 and includes a substantially cylindrical channel forreceiving the lens barrel 110. The back portion of the lens barrel 116can be used for axial alignment relative to the mount 120.

The image sensor substrate 140 comprises a printed circuit board formounting the image sensor assembly 130 and may furthermore includevarious electronic components that operate with the image sensorassembly 130 or provide external connections to other components of thecamera system. The image sensor assembly 130 houses an image sensor(e.g., a high-definition image sensor) for capturing images and/or videoand includes structural elements for physically coupling the imagesensor assembly 130 to the image sensor substrate 140 and to the cameralens mount 120. The image sensor of the image sensor assembly 130 lieson an image plane 171. The combined focal plane of the lens elements 112including the lens window and lens elements inside barrel 116 ismaintained to coincide with the image plane 171.

The lens barrel 110 is made of a material having a coefficient ofthermal expansion that causes the lens barrel 110 to expand withincreasing temperature. As a result of this expansion, the lens elements112 move further apart from each other with increasing temperature.Absent other compensation, the increased distances between the lensescause a shift in the position of the focal plane so that the image is nolonger focused at the image sensor.

In order to compensate for the shift in focal plane caused by thermalexpansion of the lens barrel 110, one or more spacers 150-151 aremounted to an inner surface of the lens barrel 110 and structured tocouple one or more of the lens elements 112 b to the lens barrel 110. Inthe illustrated example, the lens element 112 b is coupled (e.g.,mounted) to the inner surface of the lens barrel 110 via the one or morespacers 150-151 while the lenses 112 a are directly coupled (e.g.,mounted) to the inner surface of the lens barrel 110. In one embodiment,the one or more spacers 150-151 are adhered to the lens barrel 100 usingan adhesive and the lens element 112 b is then adhered to the one ormore spacers and further adhered to the lens elements 112 so that thelens element 112 b is not directly attached to the lens barrel 100. Thespacers 150-151 are made of a material which has a coefficient ofthermal expansion different from that of the material of the lens barrel110. As a result, the lens element 112 b will shift with temperature bya different amount and/or direction than the other lens elements 112 aand thereby change the position of lens element 112 b with respect tothe other lens elements 112 a. This causes a shift in the focal planeopposite the shift caused by all of the lens elements 112 a-112 b movingapart due to expansion of the lens barrel 110, thereby compensating forthe thermal effects. Particularly, the material of the spacers 150-151are chosen such that the shift in the focal plane caused by expansion ofthe lens barrel 110 is exactly or approximately compensated for by theadditional shift of the lens element 112 b relative to the other lenselements 112 a. In one embodiment, the thermal compensating elements150-151 are structured to hold only the lens elements 112 b of which themovement most substantially affects the focal plane of the lenses 112a-b. In some embodiments, the spacers 150-151 are maintained at adifferent temperature than the barrel 110 by heating or cooling of therespective parts relative to each other. In one embodiment, the spacers150-151 are a ring-shaped spacer.

FIGS. 2-4 illustrate examples of spacers 150 coupling (e.g., mounting) alens element 112 b to a lens barrel 120. Each of these views illustrateone half of a cross-sectional view, which is axisymmetric. In theembodiment of FIG. 2, the spacer 150 (e.g., a ring-shaped spacer) isadhered to the barrel 120 on one side (e.g., an outer surface) andadhered to the lens element on the opposite side (e.g., an innersurface) so that it can expand by a different amount relative to thebarrel 120. For particularly, the lens barrel 120 is shaped to includeoffset inner surfaces 222 and 223 parallel to the optical axis 170 thatmeet at a surface perpendicular or diagonal with respect to the opticalaxis 170, thus forming a corner 221. The spacer 150 may be mounted(e.g., using adhesive) to the inner surface 222 of the lens barrel 120at the corner 221. The lens element 112 b is also shaped to include acorner 212. The spacer may be mounted (e.g., using adhesive) to the lenselement 112 b at the corner 212. The spacer 150 has surfaces 251-254.For example, the surface 251 of the spacer 150 is attached to the lenselement 112 b by adhesive. The surface 253 of the spacer 150 is incontact with or in close proximity to the inner surface 222 of the lensbarrel 120 and is structured in a manner that allows the spacer 150 toexpand at a rate different from that of the lens barrel 120. The surface214 of the lens element 112 b may also be in contact with or in closeproximity to the inner surface 222 of the lens barrel 120 in a mannerthat enables the lens element 112 b to move relative to the lens barrel120 and to maintain the lens element 112 b centered inside the lensbarrel 120. Accordingly, the motion of the lenses 112 b may be in adirection and/or magnitude different from that of the lenses 112 a.

In FIG. 3, rather than gluing the spacer 150 the lens barrel 120, thelens element is glued into the spacer 150 which is structured as anoffset cylindrical sub-barrel, and this sub-barrel is then affixed tothe main lens barrel 120 using, for example, a threaded fasteningsystem. The lens barrel 120 is shaped to include offset surfacesparallel to the optical axis 170 that meet at a surface perpendicular ordiagonal with respect to the optical axis170, thus forming a corner 321.The lens barrel 120 further includes a fastening structure such asthreads 322 on its surface 326. The spacer 150 is shaped to includeoffset surfaces parallel to the optical axis 170 that meet at a surfaceperpendicular or diagonal with respect to the optical axis 170 thusforming a reciprocal corner 352 that is substantially flush with (e.g.,are in contact or in proximity with) the corner 321 of the lens barrel120. The spacer 150 further includes a fastening structure such asthreads 353 on its surface 355 that mate with (e.g., are in contact orin proximity with) the threads 322 of the lens barrel 120. The otherside of the spacer 150 further includes a corner 351 that mates with acorner of the lens element 112 b and may be further coupled, forexample, by an adhesive. The lens element 112 b is also shaped toinclude a corner 312, reciprocal to the corner 351. As such, the lenselement 112 b may be adhered to the spacer 150, for example, viaadhesive. Such a configuration allows the lens element 112 b to moverelative to the lens barrel 120 based on a different rate of thermalexpansion of the spacer 150. Accordingly, the motion of the lenses 112 bmay be different from that of the lenses 112 a in response totemperature change.

FIG. 4 illustrates another example of a spacer 150 coupling a lenselement 112 b to a lens barrel 120. In this example, rather than havinga uniform lens barrel 120 and a separate spacer 150, the spacer 150 isintegrated with the lens barrel 120. Particularly, the lens barrel 120includes multiple segments or subsections 120 a-b. The spacer 150 issandwiched between the segments or subsections 120 a and 102 b. Thesurface 451 of the spacer 150 adheres to the surface 421 of the lensbarrel segment or subsection 120 a, and the surface 452 of the spacer150 adheres to the surface 422 of the lens barrel segment or subsection120 b. The spacer 150 may be coupled to the lens barrel segments orsubsections 120 a-b via various structures such as adhesive, fasteners(e.g., hooks, joins, latches, pins, etc.), or overmold. The spacer 150is shaped to include a corner 152 and the lens element 112 b is shapedto include a reciprocal corner 412 that mates with the corner 152 (e.g.,using an adhesive). Such a configuration allows the lens element 112 bto move relative to the other lenses 112 a because the spacer 150expands at a different rate with temperature change than the otherportions 120 a, 120 b of the lens barrel 120. Accordingly, the motion ofthe lenses 112 b may be different from that of the lenses 112 a inresponse to temperature change.

In yet another embodiment, instead of using a spacer 150 with differentcoefficient of thermal expansion than the lens barrel 120, the positionof a given lens element 112 b can be adjusted relative to the otherlenses 112 a by applying a different temperature to the portion of thelens barrel 120 holding the lens element 112 b. For example, usingheating and/or cooling elements along the lens barrel 120, a portion ofthe lens barrel 120 can be kept at a different temperature than theother portions of the lens barrel 120, thereby causing one lens element112 b to move with respect to the other lenses with temperature change.The heating and/or cooling elements can be passively or activelycontrolled to compensate for the shift in the focal plane caused bythermal expansion of the lens barrel 120.

Example Camera System Configuration

FIG. 5 illustrates an embodiment of an example camera 500 that includesthe integrated image sensor and lens assembly 100 described above. Thecamera 500 comprises a camera body having a camera lens structured on afront surface of the camera body, various indicators on the front of thesurface of the camera body (such as LEDs, displays, and the like),various input mechanisms (such as buttons, switches, and touch-screenmechanisms), and electronics (e.g., imaging electronics, powerelectronics, etc.) internal to the camera body for capturing images viathe camera lens and/or performing other functions. The cameral 500 isconfigured to capture images and video, and to store captured images andvideo for subsequent display or playback. As illustrated, the camera 500includes a lens 502 configured to receive light incident upon the lensand to direct received light onto an image sensor internal to the lens.The lens 502 is enclosed by a lens ring 504, which are both part of theintegrated image sensor and lens assembly 100 discussed above.

The camera 500 can include various indicators, including the LED lights506 and the LED display 508. The camera 500 can also include buttons 510configured to allow a user of the camera to interact with the camera, toturn the camera on, and to otherwise configure the operating mode of thecamera. The camera 500 can also include a microphone 512 configured toreceive and record audio signals in conjunction with recording video.The side of the camera 500 includes an I/O interface 514.

Additional Configuration Considerations

Throughout this specification, some embodiments have used the expression“coupled” along with its derivatives. The term “coupled” as used hereinis not necessarily limited to two or more elements being in directphysical or electrical contact. Rather, the term “coupled” may alsoencompass two or more elements are not in direct contact with eachother, but yet still co-operate or interact with each other, or arestructured to provide a thermal conduction path between the elements.

Likewise, as used herein, the terms “comprises,” “comprising,”“includes,” “including,” “has,” “having” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the invention. Thisdescription should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

Finally, as used herein any reference to “one embodiment” or “anembodiment” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. The appearances of the phrase “in oneembodiment” in various places in the specification are not necessarilyall referring to the same embodiment.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative structural and functional designs for theembodiments as disclosed from the principles herein. Thus, whileparticular embodiments and applications have been illustrated anddescribed, it is to be understood that the disclosed embodiments are notlimited to the precise construction and components disclosed herein.Various modifications, changes and variations, which will be apparent tothose skilled in the art, may be made in the arrangement, operation anddetails of the method and apparatus disclosed herein without departingfrom the spirit and scope defined in the appended claims.

What is claimed is:
 1. An integrated image sensor and lens assemblycomprising: an image sensor substrate comprising an image sensor; a lensbarrel housing a set of lens elements for directing light to the imagesensor, the lens barrel having a first portion extending into thechannel of the tube portion, the lens barrel comprising a first materialthat expands with temperature increase according to a first coefficientof thermal expansion, wherein expansion of the lens barrel increasesdistances between the set of lens elements in the lens barrel and causesa first shift in a focal plane in a first direction along the opticalaxis; one or more spacers to couple a subset of the set of lens elementsto the lens barrel, the one or more spacers comprising a second materialthat expands with temperature increase according to a second coefficientof thermal expansion different than the first coefficient of thermalexpansion such that changes in temperature cause a positional shift ofthe subset of the set of lens elements relative to other lens elementsin the set of lens elements, and wherein the positional shift causes asecond shift in the focal plane in a second direction along the opticalaxis opposite the first direction.
 2. The integrated image sensor andlens assembly of claim 1, wherein the spacers and the subset of the setof lens elements are configured to maintain an optical distance betweenthe set of lens elements and the image sensor constant or substantiallyconstant.
 3. The integrated image sensor and lens assembly of claim 1,further comprising: a lens mount comprising a tube portion extendingfrom the base portion in a direction of an optical axis substantiallyperpendicular to the focal plane, the tube portion having a channel. 4.The integrated image sensor and lens assembly of claim 1, wherein thelens barrel includes a first corner and a lens element of the subset ofthe set of lens elements includes a second corner, and a spacer isshaped to mate with the first corner and the second corner.
 5. Theintegrated image sensor and lens assembly of claim 4, wherein the spacerhas a first surface and a second surface, the first surface attached tothe lens barrel at the first corner and the second surface attached tothe lens element at the second corner.
 6. The integrated image sensorand lens assembly of claim 1, wherein the lens barrel includes a firstsurface, a second surface, and a first corner, the first surface offsetto the second surface, the first surface and the second surface form thefirst corner, a lens element of the subset of the set of lens elementsincludes a second corner, and a spacer is shaped to include offsettingsurfaces, a third corner, and a fourth corner, the third cornerreciprocal to the first corner and the further corner reciprocal to thesecond corner.
 7. The integrated image sensor and lens assembly of claim6, wherein the second surface of the lens barrel includes a firstfastening structure, and a surface of the spacer includes a secondfastening structure, the second fastening structure to engage with thefirst fastening structure.
 8. The integrated image sensor and lensassembly of claim 6, wherein the first surface and the second surface ofthe lens barrel and the offset surfaces of the spacer are parallel tothe optical axis.
 9. The integrated image sensor and lens assembly ofclaim 1, wherein the lens barrel includes a first segment and a secondsegment, and a spacer is sandwiched between the first segment and thesecond segment.
 10. The integrated image sensor and lens assembly ofclaim 9, wherein the spacer includes a first corner, a lens element ofthe subset of the set of lens elements includes a second cornerreciprocal to the first corner.